Experiments will be performed upon the isolated head-brain preparation of lamprey. Intracellular recordings will be made from giant reticulospinal neurons in the brain and attempts will be made to produce long-term changes in the synaptic potentials via a classical conditioning procedure, using electrical stimulation of cranial nerves as associative stimuli. Giant reticulospinal axons which have been stimulated electrically to produce high frequency action potential activity will be examined in the electron microscope to compare the appearance of their synaptic areas with those of unstimulated control axons. Behavioral classical conditioning experiments will be performed on lamprey in a continuing, and so far unsuccessful, attempt to achieve reliable conditioning of this vertebrate species.